Industrial machinery such as backhoes, loaders, harvesters, and material handlers utilize linkage arms to connect the main body of the machinery to the material handling components. Linkage arms manipulate loaders, shovels, and other components in myriad applications such as hauling, digging, grading, and lifting. The arms allow materials to be moved relative to the body of the respective machinery. Other machinery utilize arms to support plows or blades for groundwork.
Machinery such as backhoe loaders and forest machines use multiple arms as a linkage to perform digging work. One end of the linkage is connected to an engine or motor. The other end is connected to a digging shovel. Each individual arm has a pivot for mounting to another linkage arm and mounting points for controls rods or struts. The struts control each arm in the linkage such that the shovel can be positioned and forced into the ground. As such, the linkage arms must have extremely high strength and fatigue resistance at the pivot points and throughout the structure.
Although the linkage arm may be manufactured as a solid beam, a solid beam is cumbersome, heavy, and does not make economical use of materials. The traditional approach to the manufacture of cost-effective linkage arms has been to weld multiple planar pieces of steel together to form a three-dimensional structure. The planar pieces may be welded together along their edges or faces to form load-bearing structures with minimal use of material. In applications calling for a more pleasing cosmetic appearance, the arm may be configured as a box-beam that appears as a solid object but has a hollow center. Other arms are essentially load beams with cross-sections shaped like an “I” or other such shapes.
As compared to solid arms, these arms support high load forces with a fraction of the material use and weight. Such arms, however, have several drawbacks. In particular, these linkage arms and support beams require significant welding along all the edges of the component parts which presents problems during the manufacturing and assembly processes.
The use of complex welding in the assembly process adds significant logistical problems and cost-concerns to the manufacturing process. For example, the manufacturing process for welded beams requires a long weld line to be formed along the edges of the sheets of stock material. The weld lines are the key to the structural integrity of the linkage arm and thus require a skilled welder and time.
Modern robotics can limit welding errors and decrease manufacturing time; however, such robots require significant investment and add manufacturing complexity. Welding robots are costly and cumbersome. Significant space must be allotted to the welding area and safety region around the robots. Given the size of the equipment needed for high-temperature welding, once the body shop is configured, it can not be easily moved. Furthermore, every time an engineering change is made, additional time and money investment will be required to reconfigure the manufacturing process.
Having the welding done away from the assembly line also adds to manufacturing time. Once the welds are finished, the piece must be cooled and possibly treated before being handled or moved to the assembly line.
In addition to manufacturing issues, welded beams present shipping, assembly, and repair concerns. Because the arms require skilled labor and heavy machinery to manufacture, they must be manufactured near the machine assembly line or shipped as an assembled unit. In comparison to shipping and handling of sheet stock, shipping an entire linkage arm greatly increases costs and logistical problems.
Additionally, in the field, repair of linkage arms and beams can be more inefficient than the original manufacturing process. Shipping an entire linkage arm can be costly. For this reason, when many simple structures are needed, parts are typically shipped to the site and welding is done on-site. However, this requires a highly-skilled welder to be at the site. A problem also arises from the handling and accurate positioning of the several parts in place when welding or bonding them together. The entire process can take significant time and extends downtime when a linkage arm fails.
Recently, another approach previously applied exclusively to small three-dimensional structures has gained interest as an alternative to welded structures. Such designs involve the manufacture of three-dimensional structures with conventional tools from a two-dimensional sheet. The sheet material is bent along a first line and then bent again along subsequent bend lines with reference to the previous bend lines.
The folded sheets of the Related Applications often have been used to provide three-dimensional structures including, but not limited to, electrical appliances, electronic component chassis for computers, audio receivers, televisions, motor vehicles, autos, aerospace, appliances, industrial, and other goods.
Folding technology offers many advantages over welding. In particular, it allows for easier and quicker assembly without the use of skilled labor. It also allows the part to be shipped and moved as a sheet material and later assembled quickly on-location.
Advances in folding technology have allowed the use of thicker sheet material, which greatly increases the strength of the resulting three-dimensional structure. Thus, a stable three-dimensional structure can be formed without the need for extensive welding and cumbersome tools.
One common approach to folding sheets has been to employ sheets of materials with regions designed to control the location of the bends in the sheet material by slitting or grooving the material along a bend line. U.S. Pat. No. 6,640,605 to Gitlin et al. and U.S. Pat. No. 4,628,661 to St. Louis describe exemplars of such designs.
Using a tool such as a cutting edge, thinned regions or slits may be introduced to a sheet of material to promote bending of the material about a bend line. Alternating series of slits are cut parallel to and laterally offset from a desired bend line to promote bending of the material. The material between the overlapping slits forms bending webs or straps therebetween. As the material is bent, the straps twist and plastically deform to allow the sheet to be folded along the slit portion. Since the slits can be laid out on a flat sheet of material precisely, the cumulative error from multiple bending decreases.
In addition to other limitations discussed in detail in the applications mentioned above, the slit- and groove-based bending of sheet material described by Gitlin et al. and St. Louis have several problems under loading. The stresses in the bending straps of these designs are substantial and concentrated. If the material is grooved such that the slit does not fully penetrate the material as taught by St. Louis, then the stresses on the backside or bottom web of the groove are also substantial and concentrated. As the material is bent and the straps twist, micro tears form in the strap region. Thus, the resulting material is overstressed and failures can occur along the bending region.
Additionally, groove and slit designs similar to the designs taught by Gitlin et al. and St. Louis can not withstand significant load forces. In fact, St. Louis and Gitlin et al. admittedly apply only to minimally loaded three-dimensional structures such as appliance frames, housings, or covers. In fact, Gitlin et al. and other conventional methods are directed to bending plastic or paperboard. Even if thicker material were combined with the designs of Gitlin et al. and St. Louis, the resulting three-dimensional structure could not support significant loads.
These designs are limited in application for several reasons. First, as a result of the stresses on the straps as they are twisted during bending, they are prone to failure if any significant force is applied to the structure. Second, these configurations also lack support for the faces. Loads on the structure are held primarily by the bent straps because the edges of the slits are forced away from an opposing face during bending.
In order to strengthen the strap region, the straps can be increased in length by increasing the overlap of alternating slits. As the strap length increases, however, the force of the straps pulling the sheet against an opposing face decreases. Thus, such conventional slit designs require a trade-off between reduction of stresses in the strap regions and maintaining edge-to-face contact to support the structure.
Another approach to slitting sheet material that provides greater structural integrity is described in U.S. patent Ser. No. 10/931,615, to Durney et al., hereby incorporated by reference. This design provides for a groove defining a bending strap at one end that extends obliquely across the bend line. The straps are defined so as to promote edge-to-face contact during bending. In contrast to slit designs such as Gitlin et al., the strap extends obliquely across the bend line and bends rather than twists or torques during bending. The contact of the edges with an adjacent face also provides support to the three-dimensional structure's sides far greater than the slit and groove designs taught by Gitlin et al. and St. Louis. The diverging end portions and location of the bend straps further reduces stress concentrations over such slit and groove designs.
Folded sheets generally have free or adjacent planar segments that are folded into abutting or overlapping relation and then affixed and/or joined together to stabilize the resulting structure against unfolding and to otherwise promote rigidity. The previous techniques for affixing and/or joining the planar segments of the folded sheets together have varied considerably, depending upon the application. In many instances, adjoining planar segments on either side of a bend line have been three-dimensionally fixed utilizing a third, intersecting planar segment or other intersecting structure to limit the degrees of freedom and otherwise promote rigidity between the adjoining planar segments.
Nonetheless, even this design in combination with a thick sheet material does not have sufficient strength to support high loads for use as a linkage arm or load beam. A linkage arm for industrial machinery such as hoes, loaders, and handlers generally must withstand tens of thousands of foot-pounds torque while moving in three-dimensions with minimal fatigue during the life of its use. For example, a typical digging application call for swing load capacity of over 50,000 ft-lb. swing torque at 10 rpm and load capacity of 6000 lbs.
Prior art sheet material designed to be bent into a three-dimensional structure have several limitations preventing their use in such high-load applications. First, folding displacements in general lack the rigidity of a weld. The structure is thus prone to wobble or collapse when high forces are applied.
Folding technology also does not easily allow the formation of shapes such as an “I-beam,” which has a superior ratio of strength to material use than prior folding technology shapes. Furthermore, prior art sheet designs can not accommodate load-bearing junctions, such as pivot mounts, for attachment to other structures. With respect to typical linkage arms for industrial machinery, the structure must have a portion at one end with a bore for fastening to a contiguous structure such as another linkage arm or shovel. Prior art designs do not have the strength at each end to support a shaft or fastener imposing a high lateral and torsional forces.
What is needed is a sheet material which overcomes the above and other disadvantages of known folding displacements in high-load applications. In particular, what is needed is a three-dimensional structure with the advantages of a sheet material with folding displacements but the structural integrity of a welded or solid beam.